Programmable metallization cells and methods of forming the same

ABSTRACT

A programmable metallization cell (PMC) that includes an active electrode; a nanoporous layer disposed on the active electrode, the nanoporous layer comprising a plurality of nanopores and a dielectric material; and an inert electrode disposed on the nanoporous layer. Other embodiments include forming the active electrode from silver iodide, copper iodide, silver sulfide, copper sulfide, silver selenide, or copper selenide and applying a positive bias to the active electrode that causes silver or copper to migrate into the nanopores. Methods of formation are also disclosed.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.12/269,514, filed on Nov. 12, 2008 entitled “PROGRAMMABLE METALLIZATIONCELLS AND METHODS OF FORMING THE SAME”, the disclosure of which isincorporated in its entirety by reference thereto.

BACKGROUND

The programmable metallization cell (PMC) is a new type of memory thatis a candidate to eventually replace flash memory. PMC can offer thebenefits of longer lifetimes, lower power and better memory density. AsPMC is still being developed, there remains a need for novel oradvantageous PMCs for use in memory applications.

BRIEF SUMMARY

Disclosed herein is a programmable metallization cell (PMC) thatincludes an active electrode; a nanoporous layer disposed on the activeelectrode, the nanoporous layer comprising a plurality of nanopores anda dielectric material; and an inert electrode disposed on the nanoporouslayer.

Disclosed herein is a method of forming a programmable metallizationcell (PMC), the method including the steps of forming an activeelectrode; depositing a layer of aluminum on the active electrode;oxidizing the layer of aluminum to form a nanoporous layer of aluminumoxide, the nanoporous layer including nanopores; at least partiallyfilling at least some of the nanopores in the nanoporous layer byelectroplating a conductive material; and forming an inert electrode onthe nanoporous layer of aluminum oxide.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 a is a cross sectional view of a programmable metallization cell(PMC), and FIG. 1 b is a perspective view of an exemplary nanoporouslayer of a PMC;

FIG. 2 is a cross sectional view of a programmable metallization cell(PMC) that includes an optional sink layer;

FIG. 3 is a flowchart illustrating exemplary methods for forming a PMC;

FIG. 4 is a flowchart illustrating an exemplary method for forming ananoporous layer;

FIG. 5 is a flowchart illustrating exemplary methods for forming ananoporous layer;

FIGS. 6 a through 6 d are cross-sectional views of a PMC at variousstages of manufacture;

FIG. 7 is a flowchart illustrating exemplary methods for forming a PMC;

FIGS. 8 a through 8 f are cross sectional views of a PMC at variousstages of manufacture; and

FIG. 9 is a perspective view of an illustrative memory array includingPMCs.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

Spatially related terms, including but not limited to, “lower”, “upper”,“beneath”, “below”, “above”, and “on top”, if used herein, are utilizedfor ease of description to describe spatial relationships of anelement(s) to another. Such spatially related terms encompass differentorientations of the device in use or operation in addition to theparticular orientations depicted in the figures and described herein.For example, if a cell depicted in the figures is turned over or flippedover, portions previously described as below or beneath other elementswould then be above those other elements.

As used herein, when an element, component or layer for example isdescribed as being “on” “connected to”, “coupled with” or “in contactwith” another element, component or layer, it can be directly on,directly connected to, directly coupled with, in direct contact with, orintervening elements, components or layers may be on, connected, coupledor in contact with the particular element, component or layer, forexample. When an element, component or layer for example is referred toas begin “directly on”, “directly connected to”, “directly coupledwith”, or “directly in contact with” another element, there are nointervening elements, components or layers for example.

Disclosed herein are programmable metallization cells (PMCs), devicesand arrays including PMCs, methods of forming PMCs and methods of usingPMCs.

An illustrative example of a programmable metallization cell (PMC) isdepicted in FIG. 1. An embodiment of a PMC 100 includes an activeelectrode 110, a nanoporous layer 120 and an inert electrode 130. Thenanoporous layer 120 is disposed on the active electrode 110. In anembodiment, the nanoporous layer 120 is disposed directly on the activeelectrode 110. In an embodiment, there can be one or more than one layerbetween the active electrode 110 and the nanoporous layer 120. The inertelectrode 130 is disposed on the nanoporous layer 120. In an embodiment,the inert electrode 130 is disposed directly on the nanoporous layer120. In an embodiment, there can be one or more than one layer betweenthe nanoporous layer 120 and the inert electrode 130.

The active electrode 110 can be formed of any suitable conductivematerial. In an embodiment, a suitable conductive material can includesilver (Ag) or copper (Cu). In an embodiment, the active electrode 110can be made of a material such that when a sufficient bias is appliedacross the electrodes (active electrode 110 and inert electrode 130)material of the active electrode 110 can migrate into at least a portionof the nanoporous layer 120. In an embodiment, the active electrode 110can include for example, silver iodide (AgI), silver sulfide (AgS),silver selenide (AgSe) copper iodide (CuI), copper sulfide (CuS) orcopper selenide (CuSe). Generally, the active electrode 110 can havethicknesses as are commonly utilized. In an embodiment, the activeelectrode 110 can have a thickness of from about 50 Å to about 5000 Å.

The inert electrode 130 can be formed of any suitable conductivematerial. In an embodiment, a suitable conductive material can include,but is not limited to, tungsten (W), nickel (Ni), molybdenum (Mo),platinum (Pt), gold (Au), palladium (Pd) and rhodium (Rh) for example.Generally, the inert electrode 130 can have thicknesses as are commonlyutilized. In an embodiment, the inert electrode 130 can have a thicknessof from about 50 Å to about 5000 Å.

When a positive bias is applied to the active electrode, material fromthe active electrode will migrate towards the inert electrode. Once thematerial from the active electrode comes into contact with the inertelectrode, it is reduced and electrodeposited, forming a nanowire.Formation of the nanowire(s) creates the low resistance state of thePMC. When the electrodes are oppositely biased, the atoms in thenanowires are oxidized and migrate back towards the negatively biasedactive electrode. This breaks the nanowires returning the PMC to thehigh resistance state.

The nanoporous layer 120 generally includes a plurality of pores, forexample nanopores 124 and dielectric material 122. In an embodiment, theplurality of nanopores are dispersed, randomly or uniformly, throughoutthe dielectric material. In an embodiment, the dielectric material 122can be continuous and the nanopores 124 can be dispersed within thecontinuous dielectric material 122. FIG. 1 b illustrates a perspectiveview of an exemplary nanoporous layer 120 showing the nanopores 124 andthe continuous nature of the dielectric material 122.

In an embodiment, the nanopores 124 can have uniform, substantiallyuniform, variable (or any characterization in between) diameters. In anembodiment, the nanopores 124 can have diameters in the nanometer (nm)range. In an embodiment, the nanopores can have diameters from about 2nm to about 200 nm. In an embodiment, the nanopores can have diametersfrom about 4 nm to about 100 nm. In an embodiment, the nanopores 124 canhave variable depths. In an embodiment, the nanopores 124 span theentire thickness of the nanoporous layer 120. The depth of the nanopores124 is at least partially controlled by the depth of the startingmaterial from which the nanoporous layer 120 is formed. In anembodiment, the depth of the nanopores 124 can depend at least in parton the particular properties (including, but not limited to switchingtime and switching current) that are desired in the PMC.

In an embodiment, the nanopores 124 can be regularly dispersed in thedielectric material 122. In an embodiment the nanopores 124 can berandomly dispersed in the dielectric material. In an embodiment,portions of the nanoporous layer 120 can have regions where thenanopores 124 are uniformly distributed and portions where the nanopores124 are less uniformly or even randomly distributed. The nanopores 124,if uniformly distributed can be distributed in any pattern. In anembodiment, the nanopores 124 can be distributed in a hexagonallyarranged pattern (such as that depicted in FIG. 1 b for example). Inembodiments where the nanopores 124 are uniformly distributed, thedistribution can be due entirely to the method of forming the nanoporouslayer or can be controlled before the method of forming the nanoporouslayer is undertaken.

The dielectric material 122 is at least partially controlled by thematerial from which the nanoporous layer 120 is formed. Generally, thedielectric material 122 is one that has dielectric properties, canoptionally provide mechanical stability, and can be formed as ananoporous layer. In an embodiment, the dielectric material 122 caninclude dielectric inorganic materials, such as alumina (Al₂O₃),zirconia (ZrO₂), titania (TiO₂) and mesoporous silica; polymers such aspolystyrene and electrically conductive polymers such as polypyrrole,poly(3-methylothiophene) and polyaniline. In an embodiment where thedielectric material 122 is a polymer, it can be a crosslinked polymer,such as crosslinked polystyrene.

The structure of the dielectric material 122 is generally controlled bythe distribution and shape of the nanopores 124 which is at leastpartially controlled by the way in which the nanoporous layer 120 isformed. Generally, the dielectric material 122 can have a thickness thatspans the distance from the active electrode 110 to the inert electrode130 (or any other layers that may be disposed therein). In anembodiment, the thickness of the dielectric material 122 is dependent,at least in part, on the thickness of the material from which thenanoporous layer 120 was formed, the method by which the nanoporouslayer 120 was formed and any processing steps that were carried out onthe nanoporous layer 120 during formation. In an embodiment, thedielectric material 122 has a thickness from about 100 Å to about 500 Å.

A PMC as disclosed herein can also optionally include a sink layer. APMC that includes a sink layer can be seen in FIG. 2. This exemplary PMC200 includes an active electrode 210 on which is disposed a sink layer215, a nanoporous layer 220 disposed on the sink layer 215 and an inertelectrode 230 disposed on the nanoporous layer 220. In an embodiment,the sink layer 215 can be disposed directly on the active electrode 210,the nanoporous layer 220 can be disposed directly on the sink layer 215and the inert electrode 230 can be disposed directly on the nanoporouslayer 220.

The sink layer 215 can generally function as a source of ions. In anembodiment, the sink layer 215 can include a material that is similar tothe active electrode 210. In an embodiment, the sink layer 215 and theactive electrode 210 can have an element in common. In an embodiment,the sink layer 215 can include silver (Ag) or copper (Cu). In anembodiment where the active electrode 210 can include silver iodide(AgI), silver sulfide (AgS) or silver selenide (AgSe), the sink layer215 can include silver (Ag). In an embodiment where the active electrode210 can include copper iodide (CuI), copper sulfide (CuS) or copperselenide (CuSe), the sink layer 215 can include copper (Cu). Generally,the sink layer 215 can have thicknesses as are commonly utilized. In anembodiment, the sink layer 215 can have a thickness of from about 50 Åto about 300 Å.

In an embodiment, a PMC as disclosed herein includes an active electrodethat includes silver iodide (AgI), silver sulfide (AgS), silver selenide(AgSe) copper iodide (CuI), copper sulfide (CuS), copper selenide(CuSe); a nanoporous layer disposed on the active electrode, thenanoporous layer including a plurality of nanopores and a dielectricmaterial; and an inert electrode disposed on the nanoporous layer.

When a positive bias is applied to the active electrode, material fromthe active electrode will migrate towards the inert electrode throughthe pores of the nanoporous layer. In an embodiment where the activeelectrode includes silver iodide (AgI), the silver ions (Ag⁺) from theactive electrode will migrate through the pores of the nanoporous layertowards the inert electrode. Once the material (e.g. Ag⁺) comes intocontact with the inert electrode, they will be reduced andelectrodeposited, forming a nanowire (e.g. a nanowire of silver (Ag)metal). Once the nanowires are formed across the nanoporous layer, thisis the low resistance state of the PMC. When the electrodes areoppositely biased, the atoms in the nanowires (e.g. silver (Ag)) areoxidized and migrate back towards the negatively biased activeelectrode. This breaks the nanowires returning the PMC to the highresistance state.

Reading the PMC utilizes a small voltage applied across the cell. If thenanowires are present in that cell, the resistance will be low, leadingto higher current, which is generally read as a “1”. If there are nonanowires present or the nanowires do not span the nanoporous layer, theresistance is higher, leading to low current, which is generally read asa “0”.

Erasing the cell can be carried out by applying a negative bias to theactive electrode. The metal ions will migrate away from the inertelectrode, back into the negatively-charged active electrode. Thisbreaks the linkage across the cell and increases the resistance of thePMC.

A voltage can also be applied across the PMC in order to depositconductive material in at least some of the nanopores. Depending on thevoltage applied to the active electrode, a portion of the material fromthe active electrode may deposit in the nanopores. This material may atleast partially fill at least some of the nanopores, but not form ananowire across the entire nanoporous layer. This deposited material canfunction to decrease the switching time of the PMC by partially formingthe nanowire necessary for changing the PMC from a high resistance stateto a low resistance state.

Disclosed herein is a PMC that includes an active electrode thatincludes silver iodide (AgI), silver sulfide (AgS), silver selenide(AgSe) copper iodide (CuI), copper sulfide (CuS), copper selenide(CuSe); a nanoporous layer disposed on the active electrode, thenanoporous layer including a plurality of nanopores and a dielectricmaterial, with material from the active electrode at least partiallyfilling the nanopores; and an inert electrode disposed on the nanoporouslayer.

Also disclosed herein are methods of forming PMCs. Methods of formingPMCs as disclosed herein can offer advantages over other methods offorming PMCs. Commonly utilized methods of forming PMCs utilizechalcogenide glass, which generally has to be deposited using a varietyof physical methods, such as physical vapor deposition (PVD). PVD can bean expensive technique that operates at high temperatures and pressures,utilizes costly equipment and metal targets. It also usually requiresstringent hazard monitoring. Furthermore, filling PMC materials intrench structures using PVD generally results in poor uniformity andamorphous deposits. Also, upon crystallization, chalcogenide materialsundergo a considerable volume shrinkage which further affects theuniformity of the deposit in the trenches, due to the creation of voids.The methods of forming and utilizing nanoporous layers, as describedherein, can avoid these and other disadvantages of previously utilizedmethods of forming PMCs.

FIG. 3 illustrates exemplary methods of producing a PMC as disclosedherein. The methods depicted in FIG. 3 begin with step 310, forming anactive electrode. As discussed above, the active electrode can be formedof any suitable conductive material; exemplary materials include, butare not limited to, silver iodide (AgI), silver sulfide (AgS), silverselenide (AgSe) copper iodide (CuI), copper sulfide (CuS) or copperselenide (CuSe).

The active electrode can be, but need not be formed on, partially in, orin a substrate. The substrate, if utilized, can include any substratecommonly utilized to fabricate memory devices. Exemplary substratesinclude, but are not limited to silicon, a mixture of silicon andgermanium, and other similar materials. FIG. 6 a illustrates anexemplary article after completion of this first step, FIG. 6 a does notdepict an optional substrate, but does show the active electrode 610.Generally, the active electrode 610 can be formed by using knowndeposition methods, such as for example physical vapor deposition (PVD),chemical vapor deposition (CVD), electrochemical deposition (ECD),molecular beam epitaxy (MBE) and atomic layer deposition (ALD).

One exemplary method depicted in FIG. 3 includes, as a next step,optional step 320, forming a sink layer. As discussed above, the sinklayer is an optional component of a PMC and as such, formation of thesink layer is an optional step that can, but need not be carried out. Asdiscussed above, the sink layer generally functions as a source of ions.In an embodiment, the sink layer can include a material that is similarto the active electrode; for example, silver (Ag) or copper (Cu). If thesink layer is formed in the exemplary method, it can be formed on theactive electrode; in an embodiment, it can be formed directly on theactive electrode. Generally, the sink layer can be formed using knowndeposition methods, including, but not limited to, PVD, CVD, ECD, MBEand ALD. FIG. 6 b illustrates an exemplary article that includes a sinklayer 615 disposed on (e.g. directly on) the active electrode 610.

A next step in an exemplary method, either carried out after step 310,formation of the active electrode or step 320, formation of the sinklayer; is step 330, formation of the nanoporous layer. The nanoporouslayer can be formed on (or directly on) the active electrode; or on (ordirectly on) the sink layer. FIG. 6 c illustrates an exemplary articleafter this step has been carried out. As seen in FIG. 6 c, thenanoporous layer 620 is formed on the active electrode 610 (the optionalsink layer 615 depicted in FIG. 6 b is not depicted in the articlesshown in FIGS. 6 c and 6 d); and in an embodiment directly on the activeelectrode 610. As discussed above, the nanoporous layer 620 includesnanopores 624 and dielectric material 622. Two exemplary methods offorming a nanoporous layer are illustrated in FIGS. 4 and 5.

One exemplary method of forming the nanoporous layer is throughformation and processing of diblock copolymers. Such a method generallyutilizes the self-assembled morphology of diblock copolymer thin films.Such methods are based on well-ordered equilibrium structures, which canbe controlled by macromolecular properties, scaled by the molecularweight of the components and utilized with numerous block copolymercombinations. Formation of a nanoporous layer utilizing diblockcopolymers will be demonstrated through the use of polystyrene andpolymethylmethacrylate; however, it can be carried out using otherpolymers.

The exemplary steps in FIG. 4 include step 431, formation of a diblockcopolymer. One exemplary way of forming a diblock copolymer includesoptional steps 432, forming a copolymer solution and 433, forming alayer from the copolymer solution. Step 432 can include combining thetwo polymer materials in a suitable solvent. The choice of solvents candepend, at least in part on the particular polymers utilized. In anexemplary embodiment utilizing polystyrene and polymethylmethacrylate,toluene can be utilized as a solvent. Step 433 can include forming alayer or film from the copolymer solution. In an embodiment utilizingpolystyrene and polymethylmethacrylate, a film can be formed from atoluene solution using spin casting methods.

After formation of the diblock copolymer, step 431, the next step in anexemplary method includes annealing the copolymer under an appliedelectric field. This step can function to cause cylindrical microdomainsof the two polymers to orient parallel to the electric field lines.After this step, the diblock copolymer can be characterized as a blockof one of the polymers that contains columnar deposits of the otherpolymer. After this step, the next step, step 437, includes exposing thecopolymer to UV light. This step functions to degrade the polymer thathas formed columnar deposits within the other polymer. In an embodimentwhere polystyrene and polymethylmethacrylate are utilized, thepolymethylmethacrylate will form columnar deposits within thepolystyrene, and will be broken down by the UV exposure. This willultimately form a block of polystyrene (which can be at least partiallycrosslinked by the UV light) with columnar voids (where thepolymethylmethacrylate was located before the UV exposure).

A specific method of forming a nanoporous layer utilizing diblockcopolymers can be described as follows. Polystyrene (0.71 volumefraction) and polymethylmethacrylate with a molecular weight of 39,600daltons and a polydispersity of 1.08 can be dissolved in toluene. Thesolution can then be spin-cast into a diblock copolymer film (about 1micrometer (μm) thick) onto a conducting substrate (e.g. the activeelectrode). The copolymer film can then be annealed for about 14 hours,above the glass transition temperature of both components (105° C. forpolystyrene and 115° C. for polymethylmethacrylate) or about 165° C.under an applied electric field (dc field of 30 to 40 V/μm can beapplied across the active electrode and a second conductive material,such as a Kapton film placed over the copolymer). The sample can then becooled to room temperature, the field removed and the second conductivematerial removed. Then, the diblock copolymer can be subjected toultraviolet exposure (25 J/cm²). After UV exposure, the diblockcopolymer can be rinsed, for example with acetic acid, to remove thedegraded polymethylmethacrylate. Such a method can be utilized tofabricate an array of 14 nm diameter cylindrical voids in a crosslinkedpolystyrene matrix with a lattice constant of about 24 nm.

Another method for forming a nanoporous layer includes electrochemicalprocessing (e.g. oxidation) of a conductive material, such as aluminum(Al), titanium (Ti) and zirconium (Zr). Such a method is depicted inFIG. 5 and is exemplified with respect to aluminum (Al), although othermaterials (such as titanium (Ti), zirconium (Zr) and silica (Si) forexample) can also be utilized. An initial step in such a method caninclude step 531, forming an aluminum layer. In an embodiment, thealuminum layer can have a generally uniform thickness of about 1 mm. Analuminum layer can be formed using known methods, including but notlimited to PVD, CVD, ECD, MBE and ALD. The next step, step 534, includesanodizing the aluminum layer. Generally, anodizing the aluminumfunctions to convert at least a portion of the aluminum to aluminumoxide or alumina (Al₂O₃). The process of anodizing aluminum not onlyconverts at least a portion of the aluminum to alumina but also createspores in the alumina.

In an embodiment, anodization can be carried out by submerging thealuminum layer in an acidic solution and applying a voltage to thealuminum. In an embodiment, the aluminum can function as the anode and aplatinum electrode placed in the solution can serve as the cathode. Inan embodiment, anodization can be carried out using an oxalic acidsolution (e.g. 0.3 M oxalic acid solution) and applying a constantvoltage of about 40 V for example. The process can be carried out at lowtemperatures for example, from about 2° C. to about 5° C. Thearrangement of the pores in the alumina can be controlled, at least inpart, by the conditions of anodization. In an embodiment, anodizationfor longer periods than necessary can be utilized to prepare aluminawith more ordered pores. Generally, the size of regions of highlyordered pores (which can be referred to as defect free regions) can beincreased by increasing the anodization time. The uniformity of thepores can generally be increased by increasing the thickness of thealuminum (Al) layer that is anodized.

FIG. 5 illustrates an optional step that can also be utilized toincrease the regularity of the pores in the alumina. Optional step 532includes patterning the aluminum layer before it is anodized. Patterningthe aluminum layer can function to at least partially control thelocation of the pores. Generally, a “defect” in the aluminum layer candictate where a pore will be formed within the alumina. Patterning cancreate ordered “defects” on the surface of the aluminum. Patterning canbe accomplished by for example, pretexturing the aluminum layer, byusing for example, a textured silicon carbide (SiC) molder to produceindentations on the aluminum.

After the aluminum layer is anodized (whether pre-patterned or not), thenext step, step 536, is to remove unanodized aluminum. In embodiments,there can be a portion of the aluminum which was not anodized, i.e. notconverted into alumina and through which pores were not created.Generally, a chemical method can be utilized to remove the unanodizedaluminum. In an embodiment, an acid can be utilized to remove theunanodized aluminum; for example with a saturated solution of HgCl₂. Inan embodiment, the pore size can be controlled or modified bypost-processing methods, such as treatment with an acidic solution(e.g., 5% by weigh phosphoric acid solution at 30° C.).

After formation of the nanoporous layer, step 330, the next step, step340, is to form the inert electrode. As discussed above, the inertelectrode can be formed of any suitable conductive material; such as,tungsten (W), nickel (Ni), molybdenum (Mo), platinum (Pt), gold (Au),palladium (Pd) and rhodium (Rh) for example. Generally, the inertelectrode can be formed using known deposition methods, including, butnot limited to, PVD, CVD, ECD, MBE and ALD. FIG. 6 d illustrates anarticle after formation of the inert electrode. As seen in FIG. 6 d, theinert electrode 630 can be formed on or directly on the nanoporous layer620.

FIG. 7 depicts another exemplary embodiment of a method of forming a PMCas disclosed herein. FIGS. 8 a through 8 f depict the article at variousstages of the method of making it. The first step in this exemplarymethod includes step 710, forming an active electrode. The article aftercompletion of this step is illustrated in FIG. 8 a and includes activeelectrode 810. The step of forming the active electrode, step 710, andcharacteristics of the active electrode 810 were discussed above.

FIG. 7 also depicts the next step, step 720, deposition of a conductivematerial, such as an aluminum (Al), zirconium (Zr) or titanium (Ti)layer. The article after completion of this step is illustrated in FIG.8 b and includes aluminum layer 821, disposed on, or directly on activeelectrode 810. The aluminum layer can be deposited using known methods,including but not limited to, PVD, CVD, ECD, MBE and ALD. In anembodiment, the aluminum layer can have a thickness from about 100 Å toabout 500 Å.

FIG. 7 also depicts an optional step, step 730, patterning the aluminumlayer. The article, after completion of this step is illustrated in FIG.8 c and includes defects 823 created in the aluminum layer 821. Thedefects 823 can be created by for example, pretexturing of the aluminum.The shape of the defects are not necessarily important, and the pyramidstructures illustrated in FIG. 8 c are only a non-limiting example of adefect that could be formed.

The next step, whether the optional step of patterning (step 730) wascarried out or not, is to convert the aluminum layer to a nanoporouslayer. Generally, this step can be carried out by oxidizing the aluminum(converting it to alumina, Al₂O₃ which is a dielectric material) andcreating pores within the alumina. One method of carrying this out is toanodize the aluminum in an acidic solution by application of a voltage.Specific exemplary parameters for carrying out this step were discussedabove. FIG. 8 d illustrates the article after this step has been carriedout and shows the nanoporous layer 820 disposed on, or directly on theactive electrode 810. The nanoporous layer 820 includes pores 824 anddielectric material 822.

The next step, shown in FIG. 7 includes step 750, at least partiallyfilling at least some of the nanopores with conductive material. Thestep of at least partially filling at least some of the nanopores with aconductive material can function to reduce the amount of time necessaryto switch the PMC from the high resistance state to the low resistancestate by forming at least part of the nanowire across the nanoporouslayer. FIG. 8 e depicts an article after completion of this step andshows partially filled pores 825 that are partially filled withconductive material 826.

This step can be accomplished using electrodepositing techniques. In anembodiment, conductive material can be deposited in at least a portionof the nanopores. The active electrode can function as the electrode inthe electrodeposition process, this will allow for deposition of theconductive material inside the pores only, as the dielectric material isnon-conducting. In an embodiment where the electrodeposition processresults in the nanopores being overfilled (thereby “spilling” conductivematerial onto the top surface of the nanoporous layer) furtherprocessing steps can be carried out to remove the conductive materialfrom the surface of the nanoporous layer. Such steps can include, forexample, chemical mechanical planarization (CMP). In an embodiment, theconductive material 826 can at least partially fill at least some of thenanopores. In an embodiment, the conductive material 826 can fill atleast some of the nanopores at least about 50%. In an embodiment, theconductive material 826 can fill at least some of the nanopores at leastabout 75%. In an embodiment, the conductive material 826 can at leastpartially fill a majority of the nanopores. In an embodiment, theconductive material 826 can at least partially fill substantially all ofthe nanopores.

The next step, step 760 is the formation of an inert electrode. Thearticle after completion of this step is illustrated in FIG. 8 f andincludes inert electrode 830. The inert electrode 830 can be disposed onor directly on the nanoporous layer 820. The step of forming the inertelectrode, step 760, and characteristics of the active electrode 830were discussed above.

Also disclosed herein are memory arrays that include PMCs as disclosedherein. FIG. 9 illustrates a generic array 910 having a plurality ofword lines 911 and bit lines 912 that may be orthogonal to word lines911. An exemplary word line 911 a and bit line 912 a are operativelyconnected to a PMC 914 a. The PMC 914 a may be part of a PMC structure915 which can include a plurality of PMCs 914, or can have a similarlayered structure across the entirety of the PMC structure 915, withPMCs 914 being defined only by the intersection of the word lines 911and the bit lines 912. The exemplary memory array 910 is a crosspointarray structure. A select device, such as diode or transistor, althoughnot pictured in this figure, may be present at each crosspoint.

RRAM cells as disclosed herein can be included in stand alone devices orcan be integrated or embedded in devices that utilize the RAM, includingbut not limited to microprocessors (e.g., computer systems such as a PCe.g., a notebook computer or a desktop computer or a server)microcontrollers, dedicated machines such as cameras, and video or audioplayback devices.

Thus, embodiments of PROGRAMMABLE METALLIZATION CELLS AND METHODS OFFORMING THE SAME are disclosed. The implementations described above andother implementations are within the scope of the following claims. Oneskilled in the art will appreciate that the present disclosure can bepracticed with embodiments other than those disclosed. The disclosedembodiments are presented for purposes of illustration and notlimitation, and the present disclosure is limited only by the claimsthat follow.

1. A method of forming a programmable metallization cell (PMC)comprising: forming an active electrode, the active electrode comprisingsilver iodide (AgI), silver sulfide (AgS), silver selenide (AgSe),copper iodide (CuI₂), copper sulfide (CuS), or copper selenide (CuSe);forming a nanoporous layer on the active electrode, wherein forming thenanoporous layer comprises forming a layer of aluminum having athickness of about 1 mm, the nanoporous layer comprising nanopores;forming an inert electrode on the nanoporous layer; applying a positivebias to the active electrode thereby causing silver (Ag) or copper (Cu)to migrate into the nanopores.
 2. The method according to claim 1further comprising forming a sink layer on the active electrode, thesink layer comprising silver (Ag) or copper (Cu).
 3. The methodaccording to claim 1, wherein the step of forming a nanoporous layer onthe active electrode comprises depositing a layer of conductive materialand oxidizing the conductive material.
 4. The method according to claim1, wherein the step of forming a nanoporous layer on the activeelectrode comprises depositing a layer of conductive material andanodizing the conductive material in an acidic solution by applicationof a voltage.
 5. A method of forming a programmable metallization cell(PMC) comprising: forming an active electrode; depositing a layer ofaluminum on the active electrode, the layer of aluminum being depositedto a thickness of about 1 mm; oxidizing the layer of aluminum to form ananoporous layer of aluminum oxide, the nanoporous layer comprisingnanopores; at least partially filling at least some of the nanopores inthe nanoporous layer by electroplating a conductive material; andforming an inert electrode on the nanoporous layer of aluminum oxide. 6.The method according to claim 5, wherein oxidizing the layer of aluminumcomprises anodizing the aluminum in an acidic solution by application ofa voltage.
 7. The method according to claim 5 further comprisingpatterning the layer of aluminum before oxidizing.
 8. The methodaccording to claim 5, wherein at least some of the nanopores are atleast half filled with conductive material.